In a convoy travel of vehicles, in which vehicles form a convoy by exchanging information through vehicle-to-vehicle communication, a second vehicle and subsequent vehicles in the convoy follow a leader vehicle of the convoy which travels at the forward most position in the convoy. Further, the other vehicles in the convoy should quickly respond to the change of behavior of the subject vehicle. Therefore, all vehicles in the convoy regularly at short intervals transmit information required for the other vehicles such as a current position of the vehicle and the like (i.e., convoy travel information, hereinafter). Further, in a pre-convoy stage before organizing a convoy, vehicles may also transmit the convoy travel information regularly, so that a convoy of vehicles can easily/readily be organized with other vehicles.
In the convoy travel information, the current vehicle position of the information transmitting vehicle is included. However, a convoy of vehicles may be organized with many vehicles traveling in a relatively small area and the current position of the vehicle may include errors. Therefore, it may be difficult to accurately identify the vehicle that has transmitted the convoy travel information, based only on the current vehicle position. For overcoming such difficulty, a technique disclosed, in Japanese Patent Laid-Open No. 2009-239585 uses a sender vehicle ID included in the convoy travel information, clearly identifying the sender vehicle.
However, if the vehicle ID is included in the information and such information is transmitted, it may be a breach of security and/or privacy of the vehicle that transmitted the information, and may allow other entities to identify personal information, such as, who owns the vehicle.